A support structure of this type is described, for example, in German Published Patent Application No. 199 17 177. It has a floor that, in the forward longitudinal vehicle direction, evolves into an upwardly extending front end wall and, in the rear longitudinal vehicle direction, evolves into an upwardly extending rear end wall. The support structure also has a front extension that is attached to the front end wall by front longitudinal members. The support structure further has a rear extension that is fastened to the rear end wall by rear longitudinal members.
The design of support structures is complicated, because it is often necessary to take into account conflicting requirements. Adequate crash and endurance strength must be ensured. At the same time, the support structure must have compact external dimensions and provide a relatively large vehicle interior. In the engine compartment, in particular, the design of the support structure is especially complicated, in particular, that of the front and rear longitudinal members. The tools needed to produce the support structure are equally complicated and expensive.
A self-supporting, rigid passenger enclosure for a passenger car, which is constructed of extruded profiles, the  longitudinal profile directions of which extend parallel to the longitudinal vehicle direction, is described in European Published Patent Application No. 0 538 679.
A method of designing side wall sections of a passenger enclosure in a passenger car in the form of extruded profiles, the longitudinal profile direction of which extend parallel to the longitudinal vehicle direction, is described in European Published Patent Application No. 0 622 289.
An object of the present invention is to provide an arrangement of a support structure of the type mentioned above, e.g., one that may be produced more economically.